The present invention relates to crosslinked polyurethane foam compositions. More particularly, the present invention relates to crosslinked polyurethane foam compositions having greatly enhanced wicking capabilities; i.e.; superwicking crosslinked polyurethane foam compositions.
Polyurethane foams are, of course, well known to those having ordinary skill in the art. Indeed, a voluminous body of literature has accumulated over the years as researchers explored combinations of starting materials and correlated starting materials with foam properties. Moreover, numerous efforts have been made to either modify the physical properties of polyurethane foams or to prepare specialized polyurethane foams having unique properties.
Among the properties of particular interest is the property of increased water absorbence. Polymers having this property often are referred to as hydrogels or superabsorbents.
The nature and utility of superabsorbents is illustrated by U.S. Pat. No. 4,449,997, although it will be appreciated by those having ordinary skill in the art that numerous other references also could be cited. According to this reference, an apparently desirable feature of a superabsorbent is the presence of acrylate or methacrylate groups which can be salts, amides, esters, or the free acids.
As a practical matter, many hydrogels are based on acrylate and methacrylate polymers and copolymers. See, by way of example only, U.S. Pat. Nos. 2,976,576, 3,220,960, 3,993,616, 4,154,898, 4,167,464, 4,192,727, 4,192,827, and 4,529,739. The last-cited patent is of particular interest since the disclosed water-absorbent polymers are foamed. Other hydrogels are based on starch or a modified starch, as shown by U.S. Pat. Nos. 4,069,177, 4,076,663, 4,115,332, and 4,117,222. Still other hydrogels are based on poly(oxyalkylene) glycols; see, e.g., U.S. Pat. No. 3,783,872. Hydrogels prepared from hydrolyzed crosslinked polyacrylamides and crosslinked sulfonated polystyrenes are described in U.S. Pat. No. 4,235,237. Finally, polymers based on maleic anhydride (or similar compounds) have been described in U.S. Pat. Nos. 2,988,539, 3,393,168, 3,514,419, 3,557,067, and 4,401,793. U.S. Pat. No. 3,900,378 is of interest since it describes hydrogels from radiation crosslinked blends of hydrophilic polymers and fillers, many of the polymers being those described in the foregoing patents.
Polyurethane hydrogels are, of course, known and frequently are based on the reaction of a poly(alkyleneoxy) polyol with a diisocyanate. Such reaction has been studied at length. Exemplary of such polyurethane hydrogels are the references summarized below.
U.S. Pat. No. 3,939,105 describes microporous polyurethane hydrogels. The hydrogels are the reaction products of a poly(alkyleneoxy) polyol having an average molecular weight of up to about 25,000 and organic diisocyanate which have been lightly crosslinked with water or an organic amine. In practice, the polyol is reacted with the diisocyanate to give an isocyanate-capped polyol. Before the isocyanate-capped polyol is crosslinked, a liquid nonsolvent is added thereto in an amount which will not result in precipitation. It is the addition of the nonsolvent which results in the production of the microporous hydrogel. The nonsolvent typically is an aliphatic hydrocarbon or a dialkyl ether.
The disclosure of U.S. Pat. No. 3,939,123 is similar to that of the foregoing patent, except that in the present patent a nonsolvent is not employed.
In a variation of the procedures disclosed in the two preceding patents, U.S. Pat. No. 3,940,542 describes the extrusion of the isocyanate-capped poly(alkyleneoxy) polyol of such preceding patents into a coagulant or crosslinking bath containing water or an organic polyamine as a crosslinking agent to produce water swellable, lightly crosslinked hydrogel polymer tapes or fibers. U.S. Pat. No. 4,209,605 describes another variation in which hydrogels are produced by charging preselected feeds containing the poly(alkyleneoxy) polyol, diisocyanate, and catalyst to a reaction zone, extruding the resulting high viscosity polymer through a suitable die, and allowing crosslinking to take place by exposure to atmospheric humidity.
U.S. Pat. No. 4,182,827 describes a method of increasing the wetting rates of the hydrogels disclosed in the above three patents. The wetting rates are enhanced by treating the surface of the solid hydrogel with certain ketones, alcohols, organic amines, aromatic hydrocarbons, or aqueous alkali metal hydroxide solutions.
It appears to be generally known that the best superabsorbent polymers are polyelectrolytes. That is, such superabsorbents contain a plurality of ionic groups. The preferred ionic groups are salts of carboxylic acids. Examples of carboxylate-containing polyurethanes and polyurethane hydrogels are noted below.
U.S. Pat. No. 3,412,054 describes water-dilutable polyurethanes which are useful as surface coatings and printing inks. Such polyurethanes contain carboxylic acid groups which can be neutralized with ammonia or an amine. The carboxylic acid groups are provided by incorporating into the polyurethane a 2,2-bis(hdroxymethyl)-substituted carboxylic acid. Examples of suitable acids include 2,2-bis(hydroxymethyl)acetic acid, 2,2,2-tris(hydroxymethyl)acetic acid, 2,2-bis(hydromethyl)propionic acid, 2,2-bis(hydroxymethyl)butyric acid,. 2,2-bis (hydroxymethyl) pentanoic acid, and the like. The polyurethanes are prepared by known techniques, such as adding organic diisocyanate to a mixture of a suitable carboxylic acid and a polyol polyurethane precursor.
U.S. Pat. No. 4,156,066 discloses polyurethanes characterized by lactone groups and hydroxy groups in the polymer backbone. The polyurethanes are prepared by reacting an organic polyisocyanate with a poly(alkyleneoxy) polyol and a polyfunctional lactone having excess hydroxy groups. The free hydroxy groups which are present in the formed polyurethane are available for crosslinking the polymer. See also U.S. Pat. No. 4,156,067. The lactone groups can be hydrolyzed to form free carboxylic acid groups or carboxylate groups, as taught by U.S. Pat. No. 4,255,550. The hydrolyzed polyurethane in turn can be reacted with an organic chloride in the presence of a strong base, followed by treatment with hydrochloric acid to give a polyurethane containing quaternary ammonium chloride groups. See, e.g., U.S. Pat. No. 4,451,635.
U.S. Pat. No. 3,928,299 describes the reaction of a hydroxy group-containing polymer with an unsaturated isocyanate. Suitable hydroxy group-containing polymers can be obtained by the polymerization of hydroxyalkyl esters of acrylic acid or alpha-alkyl-substituted acrylic acids or by the copolymerization of these compounds with other vinyl or vinylidene compounds. Suitable hydroxylalkyl esters are the monoesters of the foregoing acids with ethylene glycol, propylene glycol, propane-1,3-diol, butanediol, diethylene glycol, and higher polyethylene glycols. Such polymers also can be polyesters of polybasic aliphatic or aromatic carboxylic acids with polyhydric alcohols, polyurethanes which contain hydroxy groups, or epoxy resins which contain hydroxy groups. The resulting polymers are crosslinkable by vinyl polymerization and are useful for the preparation of coatings and molded products. Foams, especially polyurethane foams, are not mentioned. See also U.S. Pat. No. 4,210,713.
Disclosures similar to that of the above patent are found in U.S. Pat. Nos. 3,871,908, 3,856,830 3,954,714, and 4,082,710.
U.S. Pat. No. 4,131,602 describes radiation-curable acrylated polyurethane coating compositions. The compositions are prepared by reacting an isocyanate-terminated urethane intermediate with an amount of a hydroxyalkyl, hydroxycycloalkyl, or hydroxyaryl ester of acrylic acid or methacrylic acid which is sufficient to react with at least 80 percent of the isocyanate groups of the urethane intermediate. The urethane intermediate is the reaction product of an organic diisocyanate, an organic triol or tetraol which is either a polyester or a polyether, and an organic diol which is either a polyester or a polyether. The diisocyanate is used in an equivalent excess to the other two components. In addition, when the triol or tetraol is a polyester, the diol must be a polyether, and when the triol or tetraol is a polyether, the diol must be a polyester.
U.S. Pat. No. 4,153,778 describes acrylyl-capped urethane oligomers which readily cure by thermal or radiation means and are useful as coatings, binders, and adhesives. The oligomers are the reaction products of a poly(oxytetramethylene) diol or a polycaprolactone polyol, an organic diisocyanate, a di- or tri-methylol carboxylic acid, and an acrylyl compound.
Polyester urethane-containing molding compositions are described in U.S. Pat. No. 4,287,116. Briefly, an ethylenically unsaturated monomer solution having dissolved therein a polyester urethane resin and an organic polyol polyurethane precursor is gelled by the addition of a polyisocyanate polyurethane precursor. The gelled mixture then is molded and cured by copolymerization of the ethylenically unsaturated monomer and the resin. The resin typically is a condensation product of a dihydroxy-terminated poly(oxyalkylene) bisphenol A maleate or fumarate and a polyisocyanate which is further reacted with a hydroxy-terminated ester of acrylic or methacrylic acid. The polyol precursor is a saturated aliphatic polyol or alkoxylated derivative thereof. The ethylenically unsaturated monomer can be, by way of illustration, styrene, vinyltoluene, divinylbenzene, esters of acrylic or methacrylic acid, vinyl acetate, divinyl ether, and the like. Finally, the polyisocyanate precursor is an aliphatic, cycloaliphatic, or aromatic compound having at least two isocyanate groups.
U.S. Pat. No. 4,480,079 discloses molded plastic products which are produced by the in-mold copolymerization of methyl methacrylate with a polyurethane acrylate or methacrylate. The latter material is derived from a hydroxyalkyl acrylate or methacrylate by reaction of the hydroxy groups thereof with the isocyanate groups of either a polyisocyanate free of urethane groups and having an isocyanate functionality greater than two or a urethane polyisocyanate having an isocyanate functionality greater than two and derived from a polyisocyanate by reaction thereof with the hydroxy groups of an aliphatic alcohol having up to three hydroxy groups.
Some additional references are known which appear to relate to interpenetrating polymer networks. Consequently, such references will be noted herein without comments. The references are U.S. Pat. Nos. 4,359,558, 4,408,023, 4,424,305, 4,439,583, 4,439,584, 4,439,585, 4,454,309, 4,490,423, 4,496,535, and 4,551,486, U.K. Patent Application No. GB 2,150,938A, and European Patent Application No. 85105252.2, published as No. 0,163,150.
Acrylic monomers containing carbamate (urethane) functionality are described in U.S. Pat. Nos. 3,297,745, 3,425,988, 4,129,667, and 4,279,833. An acrylic monomer containing isocyanate functionality, isocyanatoethyl methacrylate, is described in Adhesives Age, October, 1984. The article summarizes three areas in which isocyanatoethyl methacrylate has been used: (1) applications where the methacrylate group is polymerized first, leaving the isocyanate group for a later reaction, (2) applications where the isocyanate group is reacted with a polyfunctional material first, leaving the vinyl group for a later reaction, and (3) applications where the isocyanate group is reacted with a monofunctional reagent first to make a new monomer which can be polymerized later.
Mention may be made at this point of an alternative method of achieving increased water absorbency, namely, the physical incorporation of a superabsorbent material into a polyurethane foam. This approach is illustrated by U.S. Pat. No. 3,900,030 which describes a polyurethane foam of approximately the same type as those disclosed in U.S. Pat. No. 3,903,232 et. seq. which has dispersed throughout the foam a particulate, water-swellable polymer containing a plurality of hydrophilic groups such as carboxy, carboxamide, sulfonate salt, or hydroxy groups. The particulate polymer is included to increase the water absorbency of the foam.
The use as a starting material of what may be termed polyether polyols, polyglycolethers, poly(oxyalkylene) polyols or glycols, or poly(alkyleneoxy) polyols or glycols has been studied extensively. One of the earliest references describing such materials is U.S. Pat. No. 2,948,691. According to this patent, polyglycolethers having a molecular weight of at least 500 and at least two terminal hydroxy groups can be reacted with mono- or polyfunctional isocyanates to give products which may be used for producing plasticizers, lubricants, plastics, spongy materials, gel formers, thickening agents, and the like. The patent describes the preparation of hydrogels and foams.
Subsequent studies with these poly(alkyleneoxy) polyols demonstrated a high suitability for the preparation of hydrogels and foams having particular properties, as illustrated by the references described below.
U.S. Pat. No. 3,861,993 describes a composite foam scouring pad, one component of which is a hydrophilic foam composition prepared by reacting an isocyanate-capped poly(oxyethylene) polyol having an isocyanate functionality of at least two with an aqueous solution containing a blowing agent such as a polyisocyanate, a nonionic surfactant, and, when the isocyanate-capped poly(oxyethylene) polyol isocyanate functionality is about two, a crosslinking agent. The ratio of moles of water to moles of isocyanate functionality in the polyol can range from about 6.5 to about 390. The same hydrophilic foam is employed to prepare a laminated fabric as described in U.S. Pat. No. 3,874,964 and a horticultural foam structure as described in U.S. Patent No. 3,889,417. The reticulated crosslinked polyurethane foam described in U.S. Pat. No. 3,890,254 appears to differ from that described above in that particular types of surfactants are required and the isocyanate-capped poly(oxyethylene) polyol is derived from a poly(oxyethylene) polyol having a weight average molecular weight of from about 200 to about 20,000 and a hydroxy group functionality of from about 2 to about 8. See also U.S. Pat. No. 4,160,076.
Compressed foams which are restored to their original volume in the presence of water or heat are disclosed in U.S. Pat. No. 3,903,232; see also U.S. Pat. No. 3,854,535. The foams are similar to those described in U.S. Pat. No. 3,861,993. Briefly, a moisture of from 0 to about 97 percent by weight of an isocyanate-capped hydrophilic poly(oxyethylene) polyol having an isocyanate functionality of two and an isocyanate-capped poly(oxyethylene) polyol having an isocyanate functionality of from about 3 to about 8 and a weight average molecular weight of from about 200 to about 1,500 (20,000 according to claim 1) is reacted with water, optionally in the presence of a crosslinking agent. The ratio of moles of water to moles of isocyanate groups can range from about 6.5 to about 390. See also U.S. Pat. Nos. 4,156,592 and 4,292,412 which disclose the use of such foams in the preparation of expandable fabric softener-containing articles and hydrophilic fabric softener foam compositions, respectively. Similar foams are disclosed in U.S. Pat. No. 4,110,508 and 4,137,200 in which the poly(oxyethylene) polyol moiety of the isocyanate-capped polyol has a weight average molecular weight of from about 200 to about 20,000. See also U.S. Pat. Nos. 4,201,846, 4,258,137, and 4,309,509 which describe the incorporation into the foam of U.S. Pat. No. 4,137,200 hydrophilic fibers prepared from vinyl alcohol homopolymers and copolymers, an epoxy resin, and an odorant, respectively. In addition, U.S. Pat. No. 4,127,516 describes the inclusion of a polyurea in the reaction mixture which yields the foams of U.S. Pat. No. 4,110,508. The polyurea is prepared by, for example, the reaction between a linear poly(oxyethylene) polyol which has been capped with a polyisocyanate and a polyamine in an organic solvent.
U.S. Pat. No. 3,904,557 describes a method for producing a multicolored polyurethane sponge. A poly(oxyethylene) polyol having a weight average molecular weight of from about 200 to about 20,000 and hydroxy functionality of from about 2 to about 8 is capped with a polyisocyanate. At least two distinctly different coloring agents are added to at least two different portions of isocyanate-capped polyol or water. The colored portions then are reacted with separate portions of water or isocyanate-capped polyol, respectively, to form separate colored foaming masses which then are mixed together under laminar flow conditions to yield a multicolored variegated polyurethane foam.
A polyurethane hydrogel is described in U.S. Pat. No. 4,118,354. The hydrogel is produced by dispersing into an aqueous liquid phase a product obtained by the reaction of a polyisocyanate having at least two isocyanate groups with a polyether. The polyether results from the polycondensation of at least two alkylene oxides with a polyalcohol having at least two hydroxy groups and has an average molecular weight per hydroxy group of from 1,000 to 4,000. Preferable, 75 to 85 percent of the alkylene oxides is ethylene oxide. The resulting hydrogel has a greater water content and is highly elastic and highly stable, even in the presence of a corrosive electrolyte solution.
Urethane foams having low resiliency are described in U.S. Pat. No. 4,158,087. The foams are obtained by reacting a poly(oxyalkylene) urethane prepolymer containing at least 40 mole percent of oxyethylene units in the oxyalkylene portion of the prepolymer, water, and from about 40 to about 150 parts by weight on a solids basis per 100 parts by weight of the prepolymer of a synthetic polymer latex. The prepolymer is an isocyanate-capped poly(oxyethylene) polyol of the type described in U.S. Pat. Nos. 3,903,232 et. seq.
U.S. Pat. No. 4,181,770 describes the preparation of a hydrophilic foam from an isocyanate-terminated branched polyethylene polyol, an isocyanate-terminated polyester prepolymer, a minor amount of 4,4'-diphenylmethanediisocyanate/polycarbodiimide liquid condensation product which has 30 percent free isocyanate groups, and water. The foam is stated to have improved firmness and scuff resistance properties.
Isocyanate-capped urethane-containing prepolymers prepared from polyols obtained from an epihalohydrin are described in U.S. Pat. Nos. 4,273,913 and 4,297,482. The polyol can be, for example, a polyalkylene glycol composed of the same or different oxyalkylene units or a mixture of different polyalkylene glycols.
U.S. Pat. Nos. 4,314,034, 4,365,025, 4,377,645, 4,384,050, and 4,384,051 describe variations of a general concept which involves mixing a resin phase and an aqueous phase. The resin phase comprises an isocyanate-capped poly(oxyalkylene) glycol of the type described in U.S. Pat. No. 3,903,232 et seq. and diphenylmethane diisocyanate and/or polymeric forms or isocyanate containing derivatives thereof.
While extensive research has been carried out on the preparation of polyurethane foams and superabsorbents, relatively few polyurethane foams containing a plurality of carboxylic acid groups are known. In fact, it generally is recognized that such foams are difficult to prepare; note the statement in U.S. Pat. No. 3,412,054, discussed supra. Moreover, the superabsorbent polyurethane art seems to be devoid of teachings regarding wicking rates.